The present application relates to vehicle braking systems, and is particularly directed to a drum brake dust shield for a vehicle braking system, such as a heavy vehicle braking system that includes a drum brake assembly.
A typical drum brake assembly of a heavy vehicle, such as a truck, includes a brake shoe that engages a wheel drum to transmit braking torque through a brake spider to an axle. One end of the brake shoe is pivotable against an anchor pin that is attached to one side of the brake spider. A cam follower roller is disposed at the other end of the brake shoe. When a service brake application occurs, a camshaft located on an opposite side of the brake spider is actuated to rotate about its longitudinal central axis. As the camshaft rotates about its longitudinal central axis, a cam surface of an S-cam mounted on the camshaft acts against the cam follower roller to pivot the brake shoe about the anchor pin. As the brake shoe pivots about the anchor pin, brake lining of the brake shoe frictionally engages the wheel drum to transmit braking torque through the brake spider to the axle and thereby to decelerate and brake the vehicle.
In some heavy vehicles, components within the drum brake assembly are protected from debris (e.g., road debris) so that the debris does not interfere with operation of the drum brake assembly during a service brake application. Typically, a thin-metal dust shield with a number of mounting bolt holes is fastened with bolts to the brake spider. The dust shield fills open gaps between the brake spider and the wheel drum to prevent debris from reaching the components within the drum brake assembly and thereby to prevent the debris from interfering with operation of the drum brake assembly.
The dust shield may be in the form of a single-piece annular disc that is often split almost entirely down the middle with a slit. The slit allows the dust shield to be spread apart along the slit for installation between the brake spider and the wheel drum after the brake spider and the wheel drum have already been installed on the axle. The spreading apart of the dust shield can sometimes cause enough mechanical stresses on the material at the end of the slit to yield the material of the single-piece annular disc and initiate a crack.
The crack in the material at the end of the slit can propagate until the dust shield eventually breaks apart into two pieces due to deflections of the brake spider causing deflections of the dust shield as the drum brakes are being applied during service life of the drum brake assembly. If the dust shield were to break into two pieces, the mechanical stresses on the material of the two broken pieces in the areas of the mounting bolt holes increase due to vibration loads. These mechanical stresses could increase to a level that causes loss of structural integrity of the material in the areas of the mounting bolt holes, which could then result in one or both of the broken pieces of the dust shield detaching from the brake spider and falling off of the vehicle. It would be desirable to overcome drawbacks of known drum brake dust shields.